Organic light‐emitting device dark spot growth behavior analysis by diffusion reaction theory

Dark spot growth rate tracing experiments performed on an organic light‐emitting device show that moisture entering into the device is relatively properly fitted by Fick's diffusion equation in the substrate/indium tin oxide (ITO)/hole transport layer (HTL)/silver (Ag) structure. It is believed that the moisture is dissolved into the polymer layer, which results in a decrease in the diffusion coefficient in the device with the substrate/ITO/HTL/electroluminescent (EL) polymer/Ag structure. The diffusion and chemical reaction occurring in the cathode layer further decreases the diffusion coefficient in the device with the substrate/ITO/HTL/EL polymer/calcium/Ag structure. Useful parameters, such as diffusion and solubility constants, describing possible mechanisms happening during dark spot growth on organic light‐emitting diode devices are extracted. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1697–1703, 2001     

掠射椭圆偏振谱学方法数理模型的研究

掠射椭圆偏振谱学方法通过现场测量椭圆偏振参量Δ和Ψ能够反映电极过程的性质及变化规律.将电化学反应中的扩散层模型与掠射椭圆偏振实验体系相结合,提出了掠射椭圆偏振谱学方法的数理模型,对掠射椭圆偏振参量Δ和Ψ的物理化学意义做出了解释,认为电极表面附近的溶液扩散层对于椭圆偏振光既有相位延迟器的作用,又有振幅吸收器的作用；并应用一些实验结果,分析了电解液中电活性物质浓度和入射光束斑直径对掠射椭圆偏振参量的影响.     

Micropatterned composite membranes of polymerized and fluid lipid bilayers

Micropatterned composite membranes of polymerized and fluid lipid bilayers were constructed on solid substrates. Lithographic photopolymerization of a diacetylene-containing phospholipid, 1,2-bis(10,12-tricosadiynoyl)-sn-glycero-3-phosphocholine (DiynePC), and subsequent removal of nonreacted monomers by a detergent solution (0.1 M sodium dodecyl sulfate (SDS)) yielded a patterned polymeric bilayer matrix on the substrate. Fluid lipid bilayers of phosphatidylcholine from egg yolk (egg-PC) were incorporated into the lipid-free wells surrounded by the polymeric bilayers through the process of fusion and reorganization of suspended small unilamellar vesicles. Spatial distribution of the fluid bilayers in the patterned bilayer depended on the degree of photopolymerization that in turn could be modulated by varying the applied UV irradiation dose. The polymeric bilayer domains blocked lateral diffusion of the fluid lipid bilayers and confined them in the defined areas (corrals), if the polymerization was conducted with a sufficiently large UV dose. On the other hand, lipid molecules of the fluid bilayers penetrated into the polymeric bilayer domains, if the UV dose was relatively small. A direct correlation was observed between the applied UV dose and the lateral diffusion coefficient of fluorescent marker molecules in the fluid bilayers embedded within the polymeric bilayer domains. Artificial control of lateral diffusion by polymeric bilayers may lead to the creation of complex and versatile biomimetic model membrane arrays.     

Real-time observation of dynamic heterogeneity of gold nanorods on plasma membrane with darkfield microscopy

The plasma membrane possesses a complicated structure, on which the protein clusters are randomly but orderly distributed to maintain the regular morphology and function of cells. Investigating the detailed dynamic behaviors of nanoparticles(NPs) on cytomembrane is of great importance to understand cellular mechanisms and advance the bio-nano technologies for drug delivery, photothermal therapy, immunotherapy, etc. In this work, to study the dynamic heterogeneous interactions between NPs and cell membrane with high resolution, we established a simple method to efficiently track the translational and rotational diffusion of individual gold nanorods(AuNRs) on cell membranes. This method is based on that an anisotropic AuNR appears as a colored spot under a darkfield microscope(DFM) equipped with a color camera. While obtaining its lateral position, the polar angle of the AuNR can be calculated simultaneously from intensity difference between the R and G channels. Careful analysis shows that the lateral motion of single AuNRs do not follow normal Brownian diffusion, which could be attributed to their hop diffusion in the dynamically varying picket-fence structure of the live cell membrane. Furthermore, 4 different rotationtranslation patterns of the AuNR are observed due to spatiotemporal heterogeneity of the cytomembrane. This simple but robust method for simultaneously obtaining the location and orientation of anisotropic plasmonic nanoparticles could be further applied to the analysis of complicated biological and biomedical processes.     

Photochemistry on ultrathin metal films: strongly enhanced cross sections for NO2 on Ag/Si(100)

The surface photochemistry of NO(2) on ultrathin Ag(111) films (5-60 nm) on Si(100) substrates has been studied. NO(2), forming N(2)O(4) on the surface, dissociates to release NO and NO(2) into the gas phase with translational energies exceeding the equivalent of the sample temperature. An increase of the photodesorption cross section is observed for 266 nm light when the film thickness is decreased below 30 nm despite the fact that the optical absorptivity decreases. For 4.4 nm film thickness this increase is about threefold. The data are consistent with a similar effect for 355 nm light. The reduced film thickness has no significant influence on the average translation energy of the desorbing molecules or the branching into the different channels. The increased photodesorption cross section is interpreted to result from photon absorption in the Si substrate producing electrons with no or little momenta parallel to the surface at energies where this is not allowed in Ag. It is suggested that these electrons penetrate through the Ag film despite the gap in the surface projected band structure.     

Friction force spectroscopy as a tool to study the strength and lateral diffusion of protein layers

We present a method to study the strength of layers of biological molecules in liquid medium. The method is based on the Friction Force Spectroscopy operation mode of the Atomic Force Microscope. It works by scratching the sample surface at different applied loads while registering the evolution of the sample topography and of the friction between probe and sample. Results are presented for BSA and β-casein monolayers on hydrophobic surfaces. We show how the simultaneous monitoring of topography and friction allows detecting differences not only between the strength of both types of layers, but also between the lateral diffusion of the proteins within these layers. Specifically, β-casein is shown to form stronger layers than BSA. The yield strengths calculated for both of these systems are in the range 50-70 MPa. Moreover, while no lateral diffusion is observed for BSA, we show that β-casein diffuses along the hydrophobic substrates at a rate higher than the scan velocity of the tip (16 μm s(-1) in our case).     

Photoelectrochemical Scanning Droplet Cell Microscopy (PE‐SDCM)

Principles of localised photoelectrochemistry are summarised and an experimental approach is described that allows the performance of the most important photoelectrochemical experiments within a diameter of 100 μm. Various light sources, such as a continuum emitter with a monochromator, LEDs, and lasers are coupled into a multi‐mode fibre to illuminate a small spot that is wetted by the electrolyte from a capillary. Reference electrode, counter electrode, and optical fibre are installed in the capillary system. The performance of this system is demonstrated by photocurrent measurements on n‐doped Si and p‐doped Si as model substrates. A thickness‐graded aluminium thin film for partial shadowing on Si proves the applicability for material library investigations in combinatorial materials science. Further experiments demonstrate the possibility of electrical light chopping as well as impedance spectroscopy with subsequent Mott–Schottky analysis for the determination of charge‐carrier concentration and type, flat‐band potential, and inversion layer formation. Photoelectrochemical scanning droplet cell microscopy (PE‐SDCM) is an extremely versatile tool for the screening of water splitting photoelectrodes, the characterisation of photocatalysts, and high throughput characterisation of microgram amounts of new solar cell materials.     

基于随机行走的二维空间扩散模拟研究

分子的扩散行为是微观化学的重要研究领域. 影响扩散行为的因素很多,但是目前各个因素的具体影响效果还不明确. 作者基于随机行走理论建立了分子在二维空间的扩散模型,依据此模型自主开发了模拟软件以及数据分析系统,并利用该模拟软件系统研究了势垒尧横向速度等因素对扩散行为的影响,验证了该模型的可靠性,证明根据该模型可以得到和实验尧理论相吻合的结果. 该软件有望成为模拟微观化学扩散行为的潜在平台,如电化学以及膜过滤过程中的扩散.     

Enhancement of electron transport in nano-porous TiO2 electrodes by dye adsorption

Influence of dye adsorption on electron transport in nano-porous TiO₂ electrodes filled with electrolytes is studied with various TiO₂ films and electrolytes. Electron diffusion coefficient in the electrodes is derived from pulsed laser induced current transients. It is found that dye adsorption increases the diffusion coefficients in the electrodes regardless of the difference of electrolytes and TiO₂ electrodes. The degree of the increases scales with the surface area of the nano-porous electrodes. Based on trapping model, these observations can be interpreted with that the charge traps located on the electrode surface are removed by the dye adsorption. However, dependency of electron diffusion coefficients on light intensity is not affected by dye adsorption, implying that the traps are located not only on the surface but also inside the electrodes.     

Low-picomolar limits of detection using high-power light-emitting diodes for fluorescence

Fluorescence detectors are ever more frequently being used with light-emitting diodes (LEDs) as the light source. Technological advances in the solid-state lighting industry have produced LEDs which are also suitable tools in analytical measurements. LEDs are now available which deliver 700 mW of radiometric power. While this greater light power can increase the fluorescence signal, it is not trivial to make proper use of this light. This new generation of LEDs has a large emitting area and a highly divergent beam. This presents a classic problem in optics where one must choose between either a small focused light spot, or high light collection efficiency. We have selected for light collection efficiency, which yields a light spot somewhat larger than the emitting area of the LED. This light is focused onto a flow cell. Increasing the detector cell internal diameter (i.d.) produces gains in (sensitivity)3. However, since the detector cell i.d. is smaller than the LED spot size, scattering of excitation light towards the detector remains a significant source of background signal. This can be minimized through the use of spectral filters and spatial filters in the form of pinholes. The detector produced a limit of detection (LOD) of 3 pM, which is roughly three orders of magnitude lower than other reports of LED-based fluorescence detectors. Furthermore, this LOD comes within a factor of six of much more expensive laser-based fluorescence systems. This detector has been used to monitor a separation from a gel filtration column of fluorescently labeled BSA from residual labeling reagent. The LOD of fluorescently labeled BSA is 25 pM.     

Use of a scientific microwave apparatus for rapid optimization of reaction conditions in a monomode function and then substrate screening in a multimode function

Recently, a new apparatus has become available, which aims to bring together in one unit the advantages of a monomode and a multimode microwave device. We have assessed the applicability of the apparatus toward rapid optimization of reaction conditions in a monomode function and then substrate screening in a multimode function. We have also probed the effects of differences in microwave absorptivity of reaction mixtures on the product conversions in screening multiple substrates simultaneously in a multimode microwave apparatus. We find that when the microwave absorptivity of a reaction mixture is dictated by the solvent, there is little effect on the heating profile of varying the substrate in a screening run. However, this is not the case when reactions involving non-microwave absorbant solvents are used. In this case the characteristics of the substrate can affect significantly the outcome of the reaction.     

A new wetting mechanism based upon triple contact line pinning

The classical Wenzel and Cassie models fail to give a physical explanation of such phenomenon as the macroscopic contact angle actually being equal to the Young's contact angle if there is a spot (surface defect) inside the droplet. Here, we derive the expression of the macroscopic contact angle for this special substrate in use of the principle of least potential energy, and our analytical results are in good agreement with the experimental data. Our findings also suggest that it is the triple contact line (TCL) rather than the contact area that dominates the contact angle. Therefore a new model based upon the TCL pinning is developed to explain the different wetting properties of the Wenzel and Cassie models for hydrophilic and hydrophobic cases. Moreover, the new model predicts the macroscopic contact angle in a broader range accurately, which is consistent with the existing experimental findings. This study revisits the fundamentals of wetting on rough substrates. The new model derived will help to design better superhydrophobic materials and provide the prediction required to engineer novel microfluidic devices.     

Lipid lateral mobility and membrane phase structure modulation by protein binding

Using a combination of fluorescence correlation and infrared absorption spectroscopies, we characterize lipid lateral diffusion and membrane phase structure as a function of protein binding to the membrane surface. In a supported membrane configuration, cholera toxin binding to the pentasaccharaide headgroup of membrane-incorporated GM1 lipid alters the long-range lateral diffusion of fluorescently labeled probe lipids, which are not involved in the binding interaction. This effect is prominently amplified near the gel-fluid transition temperature, Tm, of the majority lipid component. At temperatures near Tm, large changes in probe lipid diffusion are measured at average protein coverage densities as low as 0.02 area fraction. Spectral shifts of the methylene symmetric and asymmetric stretching modes in the lipid acyl chain confirm that protein binding alters the fraction of lipid in the gel phase.     

Effects of polymer structure on reactivity of functional groups in reduction reaction using tin hydride soluble supports

The influence of macromolecular chains onto reactivity of the grafted functional group has been investigated through reduction of 6‐bromohexene using tin hydride soluble polymer supports. Kinetic investigations clearly indicate a retarding effect of the polymer structure on the substrate diffusion. Correlations of molecular weight and degree of functionalization with reactivity of the functional lateral groups are discussed. In dilute regime, an increasing of internal density of the polymer coil leads to a diminution of the rate constant k_H. Thus, the higher density of the coil limits the substrates diffusion, which favors the radical cyclization and so formation of the cyclic product. At the opposite, in concentrated regime formation of the acyclic product, hex‐1‐ene is favored despite the higher viscosity of such medium that should limit the diffusion. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5954–5964, 2006     

Structure formation in bis(terpyridine) derivative adlayers: molecule-substrate versus molecule-molecule interactions

The influence of the substrate and the deposition conditions-vapor deposition versus deposition from solution-on the structures formed upon self-assembly of deposited bis(terpyridine) derivative (2,4'-BTP) monolayers on different hexagonal substrates, including highly oriented pyrolytic graphite (HOPG), Au(111), and (111)-oriented Ag thin films, was investigated by high-resolution scanning tunneling microscopy and by model calculations of the intermolecular energies and the lateral corrugation of the substrate-adsorbate interaction. Similar quasi-quadratic network structures with almost the same lattice constants obtained on all substrates are essentially identical to the optimum configuration expected from an optimization of the adlayer structure with C-H...N-type bridging bonds as a structure-determining factor, which underlines a key role of the intermolecular interactions in adlayer order. Slight distortions from the optimum values to form commensurate adlayer structures on the metal substrates and the preferential orientation of the adlayer with respect to the substrate are attributed to the substrate-adsorbate interactions, specifically, the lateral corrugation in the substrate-adsorbate interaction upon lateral displacement and rotation of the adsorbed BTP molecules. The fact that similar adlayer structures are obtained on HOPG under ultrahigh vacuum conditions (solid|gas interface) and on HOPG in trichlorobenzene (solid|liquid interface) indicates that the intermolecular interactions are not severely affected by the solvent.     

一种便携式有毒气体被动采样检测装置的研制

以甲醛作为目标物,提出了一种基于扩散原理的具有大面积表面暴露的快速被动采样器及快速测定装置。该采样器不要求任何辅助采样泵使用该采样器研发的快速测定装置适用于现场气体样品的采集与测定。     

Morphology Tailoring of Thin Film Block Copolymers on Patterned Substrates

It is well known that chemically patterned substrates can direct the assembly of adsorbed layers or thin films of block copolymers. For a cylinder‐forming diblock copolymer on periodically spot‐patterned substrates, the morphology of the block copolymer follows the pattern at the substrate; however, with different periodic spacing and spot size of the pattern, novel morphologies can be created. Specifically, we have demonstrated that new morphologies that are absent in the bulk system can be tailored by judiciously varying the mismatch between the width of the pattern and the periodic spacing of the bulk block copolymer, the top surface affinity, and spot size. New morphologies can thus be achieved, such as honeycomb and ring structures, which do not appear in the bulk system. These results demonstrate a promising strategy for fabrication of new nanostructures from chemically patterned substrates.     

Surface diffusion of metal atoms on polymer substrates during physical vapour deposition

 The surface diffusion of physical-vapour-deposited metal atoms on thermoplastic polymer substrates was investigated. In accordance with the hypothesis of the “classical” atomistic diffusion model, diffusion coefficients are derived from a Monte Carlo simulation. Because the “classical” atomistic diffusion model neglects the desorption of the metal atoms, the absolute diffusion data obtained in our investigations should only be considered as rough estimates. It is more the intention of our work to present relative values in order to correlate the metal surface diffusion on polymer substrates with their physical states (morphologies and surface dynamics). As expected, the diffusivity of metal atoms is strongly influenced by the chemical affinity (“reactivity”) between the metal atoms and the polymer substrate. Furthermore, the diffusivity strongly depends on the physical state of the polymer substrate. On polymer surfaces above the glass-transition temperature the surface diffusivity of metal atoms is 1 order of magnitude higher than the diffusivity below the glass-transition temperature. Received: 9 April 1999/Accepted in revised form: 21 October 1999     

Etude quantitative par absorption optique de l'homogeneite de monocristaux d'arseniure de gallium

The optical absorption coeffient of n-type gallium arsenide is measured at many places of samples with an infrared microscope (spot of 100 × 100 μm) and variable energies for the incident light. The inhomogeneities we observed are associated with free carrier density fluctuations in heavily doped single crystals and with the impurities diffusion around dislocations in lower ones.